1. Field of the Invention
The present invention relates to a transverse-mounted membrane filtration apparatus to which an air diffusion device removing fouling substances from a membrane element such as ceramics or the like is attached.
2. Description of the Related Art
Active sludge treatment of wastewater is a process of making active sludge absorb biochemical oxygen demand (BOD) of wastewater in an aeration tank, causing the treated water fed from the aeration tank to be subjected to a solid-liquid separation in the precipitation tank by gravity settling, and collecting supernatant liquid as treated water. However the process of solid-liquid separation making use of gravity settling takes a lot of time, and in some cases, a solid-liquid separation is impossible because of bulking (of sludge) depending on the quality of water in the tank.
Based on such background, an immersed-membrane-bioreactor method is proposed for conducting solid-liquid separation in which a membrane module, in a casing of which a membrane element such as ceramic or the like is loaded, is immersed in wastewater in an aeration tank, and filtering the wastewater in the aeration tank directly (see Japanese Laid-open Patent Publication No. H11-333490). This method is capable of solid-liquid separation without consuming a lot of time and is regardless of the quality of the water in the tank. However, the method requires a great deal of labor because the membrane module is immersed in the wastewater in the aeration tank, and thus the water in the aeration tank must be drained fully when maintaining the membrane module.
To address this, a method is proposed in recent years in which cross-flow filtration of wastewater in an aeration tank is conducted by making use of a membrane module disposed outside the aeration tank. In this method, the wastewater in the aeration tank is fed to a membrane module disposed outside by making use of a pump, and the cross-flow filtration is conducted to the wastewater by the membrane module to collect filtrate water being filtered through a membrane surface formed as a flow-path's inner periphery of the membrane element as treated water and meanwhile to return wastewater not having been filtered through the membrane surface to the aeration tank as concentrated water.